Distraction is a common surgical procedure to operate on the spine. It is used to prepare a spine for fusing two opposing (adjacent) vertebrae or to install an implant in the disc space between two opposing vertebrae. Distraction can be performed anteriorly (from the front of the patient) or posteriorly (from the back). But regardless of the approach, the procedure generally begins by first exposing that portion of the spine, which the surgeon has determined to require repair, and then removing all or part of the damaged spinal disc between the two opposing vertebrae in question.
After removing the spinal disc, the surgeon then typically inserts what the layperson may describe as one or more wedges between the two vertebrae. Each wedge is mounted on the end of a shaft and successively taller wedges are inserted between the two vertebrae until the surgeon obtains the desired separation ("distraction") between them. Once the desired separation is obtained, the surgeon then slides what the layperson may describe as a special tube over the shaft while the last wedge is still located between the vertebrae. This special tube is often referred to as a "guide sleeve". The guide sleeve is generally taller than the wedge that separates the vertebrae. Hence, the distal end (the end toward the patient) of the guide sleeve butts against the outside of the top and bottom vertebrae. Typically, the guide sleeve has a top spike and bottom spike that extend from its distal end, and these spikes are respectively placed in contact with the top and bottom vertebrae. Further, the end of the guide sleeve may have lateral extensions to extend into the disc space between the top and bottom vertebrae and around each side of the wedge. The spikes are then driven into the vertebrae by striking the proximal end of the outside sleeve distractor with a hammer or some other impact device. With the spikes placed into the vertebrae and the lateral extensions slid in the disc space, the wedge is no longer necessary to hold the vertebrae apart. The spikes and lateral extensions now serve that function, and the wedge can be pulled out from the disc space through the inside of the guide sleeve. With the wedge removed, the surgeon is then free to work through the inside of this special tube to prepare the disc space for fusion or install implants.
With the foregoing explanation in mind, some nomenclature is important to fully understand the following specification. If the wedge/tip used to separate the vertebrae is approximately as tall as it is wide, the operation is called a "single barrel" procedure. Alternatively, if the wedge/tip is approximately twice as wide as it is tall, the operation is called a "double barrel" procedure. This terminology has largely risen for metaphoric reasons. The cross-section of a guide sleeve used in a double-barrel procedure resembles the cross-section of a double-barrel shotgun, and the cross-section of the guide sleeve used in a single-barrel procedure resembles the cross-section of a single-barrel shotgun.
The insertion location of the wedges between the vertebrae is of critical importance in most any surgery involving vertebral distraction. The wedge/tip determines the placement of the guide sleeve, which in turn commonly determines the exact placement of an implant or fusion material within the disc space. Hence, prior art devices, such as that presented in U.S. Pat. No. 5,484,437 to Michelson seek to limit inadvertent migration of the wedge by incorporating sharp pegs into the top and bottom sides of the wedge. The pegs in that design, however, do not contact vertebral tissue until the distractor/wedge has all but fully separated the vertebrae in question. As a result, that prior art design may allow the distractor/wedge to migrate during insertion into the vertebral space, before the sharp pegs have the opportunity to function.
What is needed is a medical device that can immediately secure its position within the disc space between two vertebral bodies, once the surgeon places the device in contact with the spine. The following devices address this need.